1. Field of the Invention (Technical Field)
The invention disclosed herein generally relates to fluoroiodocarbon compositions of matter, and methods of making and using such compositions of matter.
2. Background Art
Chlorofluorocarbons (CFCs) such as CFC-11, CFC-12, CFC-113, CFC114, CFC-115, and blends containing these CFCs such as R-500 and R-502 are currently used as refrigerants, solvents, foam blowing agents, and propellants. CFCs contain only chlorine, fluorine, and carbon, and have the general formula C.sub.x Cl.sub.y F.sub.z, where X=1 or 2 and Y+Z=2X +2. A related group of chemicals known as halons (also called bromofiuorocarbons, BFCs), having the general formula C.sub.w Br.sub.x Cl.sub.y F.sub.z (where W=1 or 2, Y=0 or 1, and X+Y+Z=2W+2) are in current use as firefighting agents.
Because of the great chemical stability of CFCs and halons, when they are released to the atmosphere only minuscule fractions are destroyed by natural processes in the troposphere. As a result, CFCs and halons have long atmospheric lifetimes and migrate to the stratosphere where they undergo photolysis, forming chlorine and bromine radicals that seriously deplete the earth's protective ozone layer. Each chemical is assigned an ozone-depletion potential (ODP) that reflects its quantitative ability to destroy stratospheric ozone. The ozone depletion potential is calculated in each case relative to CFC-11 (CFCl.sub.3, trichloro-fluoromethane), which has been assigned a value of 1.0. Currently used CFCs have ODPs near 1; halons have ODPs between 2 and 14. Names, formulas, and ODPs of commonly used CFCs and halons are shown in Table 1.
TABLE 1 __________________________________________________________________________ NAMES, FORMULAS, AND ODPs OF CFCS IN CURRENT USE AS REFRIGERANTS, SOLVENTS, FOAM BLOWING AGENTS, AND PROPELLANTS. CFC or Halon Name Formula ODP __________________________________________________________________________ CFC-11 trichlorofluoromethane CCl.sub.3 F 1.0 CFC-12 dichlorodifluoromethane CCl.sub.2 F.sub.2 1.0 CFC-113 1,1,2-trichloro-1,2,2-trifluoroethane CCl.sub.2 FCClF.sub.2 1.1 CFC-114 1,2-dichloro-1,1,2,2-tetrafluoroethane CClF.sub.2 CClF.sub.2 0.8 CFC-115 chloropentafluoroethane CClF.sub.2 CF.sub.3 0.5 R-500 --.sup.a -- 0.3 R-502 --.sup.b -- 0.7 Halon 1211 bromochlorodifluoromethane CBrClF.sub.2 4.1 Halon 1301 bromotrifluoromethane CBrF.sub.3 12.5 Halon 2402 1,2-dibromotetrafluoroethane CBrF.sub.2 CBrF.sub.2 3.9 __________________________________________________________________________ .sup.a azeotropic blend of CCl.sub.2 F.sub.2 (CFC12, 73.8 wt. %) and CHF.sub.2 CF.sub.3 (HFC125, 26.2 wt. %). .sup.b azeotropic blend of CClF.sub.2 CF.sub.3 (CFC115, 51.2 wt. %) and CHClF.sub.2 (HCFC22, 48.8 wt. %).
CFC-12, for example, comprises approximately 26% by weight of worldwide CFC production, and about 150 million pounds per year are produced. The vast majority of this CFC-12 is eventually released to the atmosphere, where it rises to the stratosphere, is struck by ultraviolet radiation, and decomposes to give chlorine radicals that catalytically destroy the protective ozone layer of the earth. This depletion of stratospheric ozone allows more ultraviolet light to reach the surface of the earth, resulting in increases in human skin cancer and cataracts plus damage to crops, natural ecosystems, and materials, in addition to other adverse effects. This invention will significantly decrease these adverse effects by providing environmentally safe alternative agents to use in place of CFCs and halons.
At present, CFCs, in addition to selected hydrochlorofluorocarbons (HCFCs) and hydrofluorocarbons (HFCs) are used as refrigerants, solvents, foam blowing agents, and propellants. CFCs have been widely used for these applications because of their effectiveness, low toxicity, nonflammability, electrical nonconductivity, cleanliness on evaporation, miscibility with hydrocarbon and mineral oil lubricants, and relative nonreactivity towards copper, aluminum, and ferrous metals. However, CFCs are being phased out of production in the U.S. under the provisions of the Montreal Protocol, the Clean Air Act Amendments of 1990, and the presidential directive of 11 Feb. 1992. Although HCFCs (with ODPs ranging from 0.02 to 0.11) deplete ozone much less than CFCs, HCFCs do cause some ozone depletion and are also scheduled to be phased out of production eventually under the Montreal Protocol.
The broad class of halocarbons consists of all molecules that contain carbon, may contain hydrogen, and contain at least one of the following halogen atoms: fluorine, chlorine, bromine, or iodine. Iodocarbons are halocarbons that contain iodine; fluoroiodocarbons contain both fluorine and iodine. Haloalkanes are a subset of halocarbons comprising compounds made up of only carbon, halogens, and possibly hydrogen, and having no oxygen, nitrogen, or multiple bonds. In principle, haloalkanes may be derived from hydrocarbons by substitution of halogen atoms (F, Cl, Br, or I) for hydrogen atoms. Hydrocarbons themselves have been used as very effective refrigerants, solvents, foam blowing agents, and propellants but have the major disadvantage of extremely high flammability. Substitution with a high proportion of halogen atoms imparts nonflammability. CFCs and other highly halogenated halocarbons therefore possess many of the desirable properties of hydrocarbons plus the substantial advantage of nonflammability.
Toxicity is a major issue in the selection of refrigerants, solvents, foam blowing agents, propellants, and firefighting agents. For example, the toxic effects of haloalkanes include stimulation or suppression of the central nervous system, initiation of cardiac arrythmias, and sensitization of the heart to adrenaline. Inhalation of haloalkanes can cause bronchoconstriction, reduce pulmonary compliance, depress respiratory volume, reduce mean arterial blood pressure, and produce tachycardia. Long term effects can include hepatotoxicity, mutagenesis, teratogenesis, and carcinogenicity.
Environmental effects of halocarbons including ozone-depletion potential (ODP), global warming potential (GWP), and terrestrial impacts must be considered. Chlorine- and bromine-containing haloalkanes are known to deplete stratospheric ozone, with bromine posing a greater problem (per atom) than chlorine. The depletion of ozone in the stratosphere results in increased levels of ultraviolet radiation at the surface of the earth, causing increased incidences of skin cancer, cataracts, suppression of human immune systems, crop damage, and damage to aquatic organisms. These problems are considered so serious that the Montreal Protocol and other legislation have placed restrictions on the production and use of volatile halogenated alkanes.
Flame suppression occurs by two mechanisms: physical and chemical. The physical mechanism involves heat absorption by the molecules sufficient to lower the temperature of the combusting materials below the ignition point and/or displacement of oxygen thereby terminating combustion. The larger the extinguishant molecule (the more atoms and bonds it contains) the more degrees of vibrational freedom it has, the higher the vapor heat capacity, and the greater the heat removal. The chemical mechanism involves interruption of free radical flame-propagation chain reactions involving hydrogen, oxygen, and hydroxyl radicals. It has been speculated (but not proven) that bromine atoms disrupt these chain reactions.
Previous firefighting agents utilized either chemical or physical action or both to achieve flame extinguishment. Agents such as carbon dioxide displace oxygen and also absorb thermal energy. Agents such as water function solely by thermal energy absorption. Previous halogenated agents such as carbon tetrachloride, bromotrifluoromethane, etc. employ both functional means. U.S. Army studies on halogenated agents in the 1940's resulted in the adoption of the well known Halon family of agents. Other work by New Mexico Engineering Research Institute has identified neat perfluorocarbons and some neat iodinated agents as having future potential as firefighting agents (Nimitz et al., "Clean Tropodegradable Fire Extinguishing Agents with Low Ozone Depletion and Global Warming Potentials," co-pending U.S. patent application Ser. No. 07/800,532 filed by Nimitz et al. on Nov. 27, 1991). In this work a few iodine-containing chemicals in neat form were shown to exhibit similar extinguishment properties to bromine-containing chemicals.
There are many concerns regarding brominated, perfluorinated, and neat iodinated agents. Brominated agents are presently being eliminated from worldwide production, pursuant to the adoption of the Montreal Protocol and the Clean Air Act of 1990, due to their tremendous potential to destroy the stratospheric ozone layer. Perfluorinated agents have high global warming potential and atmospheric lifetimes estimated to be several thousand years. Their production and use is being restricted by pending legislation and liability concerns of current manufacturers. The costs of perfluorocarbons are high and their firefighting performance is less than that of the brominated agents. In weight and volume critical situations such as aircraft, tanks, and ships, the additional quantity required for extinguishment cannot be tolerated. One neat iodinated agent (trifluoroiodomethane, CF.sub.3 I) has long been known to have firefighting potential (Dictionary of Organic Compounds, Chapman and Hall, New York, 1982, p. 5477). Concerns about CF.sub.3 I revolve around toxicity and dispersion effectiveness. Bromotrifluoromethane (CF.sub.3 Br) was the choice agent for such gaseous flooding applications and has remained so until the present time.
Refrigerants, solvents, foam blowing agents, propellants, and firefighting agents must be chemically stable during storage and use over long periods of time and must be unreactive with the containment systems in which they are housed. Refrigerants normally operate between the temperature extremes of -98.degree. C. to 8.degree. C. The majority of residential, commercial, and institutional applications lie in the range of -23.degree. C. to 8.degree. C. In extraordinary cases (e.g., motor burnout) higher temperatures may be experienced, but in such cases the formation of other contaminants would make replacement of the fluid necessary anyway. Although solvents, foam blowing agents, and propellants are normally stored and used at room temperature, they may under unusual circumstances experience transient temperatures up to 150.degree. C. during storage. Firefighting agents must be stable on storage at temperatures of -20.degree. C. to 50.degree. C., and should decompose at flame temperatures to yield radical-trapping species.
A refrigerant operates by absorbing heat as it evaporates in one region of the apparatus, then gives up the heat as it recondenses in another portion of the apparatus. The required properties for effectiveness include appropriate vapor pressure curves, enthalpies of vaporization, solubility behavior (including oil miscibility), toxicity, and flammability. CFCs 12, 114, 500, and 502 have been used as refrigerants for many years because they possess the required physical properties such as appropriate boiling points and operating pressures, enthalpies of vaporization, miscibility with mineral oil-based lubricants, low toxicity and nonflammability. In addition, CFCs are relatively noncorrosive to metals and seal materials. Properties of commonly-used refrigerants (including typical evaporator and condenser temperatures and typical usages) are set forth in Table 2.
TABLE 2 ______________________________________ TYPICAL EVAPORATOR AND CONDENSER TEMPERATURES FOR CFC REFRIGERANTS CFC Evap. Temp (F.degree.) Cond. Temp (F.degree.) Typical Usages ______________________________________ 11 35 to 40 95 to 105 Centrifugal chillers, solvent, foam agent 12 -10 to 35 105 to 125 Auto A/C, freezers, window A/C units 13 -50 to -75 100 to 125 Very low temp freezers 113 35 to 40 95 to 105 Centrifugal chillers, solvent, cleaner 114 -24 to 35 100 to 125 Marine chillers, low temp freezers 115 -50 100 to 125 Low temp freezers 500 -30 to -80 100 to 125 Supermarket cases, vending machines, commercial transport 502 -40 to -100 100 to 125 Low temp refrigeration 503 -100 to -200 100 to 125 Cryogenic freezers ______________________________________
Hydrocarbons including cyclopropane, propane, butane, and isobutane have also been used as highly effective refrigerants. However, hydrocarbons have found little commercial use as refrigerants because of their high flammability. They possess all of the other required properties The ASHRAE Standard 15 limits the use of most hydrocarbons as Class 2 or 3 refrigerants, limiting their use to laboratory equipment with a total charge of less than 3 pounds or to technical/industrial applications wherein the refrigeration equipment is located remotely from inhabited buildings. These restrictions severely limit the current utility of refrigerants containing hydrocarbons.
Refrigeration equipment requires lubricant constantly circulating in the refrigerant fluid to avoid friction, overheating, and burnout of the compressor or bearings. Therefore miscibility of refrigerants with lubricants is an essential requirement. For example, most lubricants are not very soluble in hydrofluorocarbons (HFCs), and this has presented major problems in the use of the alternative agent HFC-134a for refrigeration.
Many billions of dollars worth of installed refrigeration and air-conditioning equipment currently exists. If CFCs become unavailable and no drop-in replacements are available, much of this equipment will be rendered inoperable and may wind up in landfills. The useful lifetime will be shortened drastically, and a significant fraction of the energy and resources put into manufacturing and installing the equipment will be wasted.
A solvent must dissolve hydrophobic soils such as oils, greases, and waxes, should be nonflammable and relatively nontoxic, and should evaporate cleanly. For solvents, chemicals with boiling points between 35.degree. C. and 120.degree. C. are preferred, because this boiling point range allows evaporation in reasonable time (between one minute and two hours). Traditionally, CFC-113 and 1,1,1-trichloroethane have been solvents of choice. Recently, because of environmental concerns about halogenated solvents, interest in hydrocarbon solvents such as Stoddard solvent (a petroleum fraction of eight- to eleven-carbon hydrocarbons) has revived, despite the flammability of these solvents. When referring to hydrocarbon petroleum fractions, it is commonly understood that the terms ligroin, mineral spirits, naphtha, petroleum ether, and petroleum spirits may represent fractions with similar compositions and may at times be used interchangeably.
A foam blowing agent must create uniform, controllable cell size in a polymer matrix, and preferably should provide high insulation value and be nonflammable. For foam blowing a wide variety of agents has been used, including CFC-11, HCFC-22, HCFC-123, HFC-134a, HCFC-141b, and pentane. Water is often added in the foam blowing agent (up to about 25% by moles) to react with the forming polymer, liberating carbon dioxide and aiding cell formation. More recently, some manufacturers have shifted to using water as the exclusive blowing agent, despite slight losses in insulating ability, dimensional stability, and resistance to aging.
An aerosol propellant must have a high vapor pressure, low heat of vaporization, and stability on storage. In the U.S., CFCs were used as propellants until 1978, and in many countries CFCs are still in use for this purpose. The continued use of CFC aerosol propellants overseas contributes substantially to stratospheric ozone depletion. After 1978 in the U.S. CFCs were replaced by the hydrocarbons butane and isobutane for many propeIlant applications. These gases are extremely flammable and people have been burned in fires involving these propellants.
Firefighting agents to replace halons must be effective extinguishants, relatively nontoxic, electrically nonconductive, must evaporate cleanly, and must have low environmental impact. Halons (bromofluorocarbons), although they meet the first four criteria, have long atmospheric lifetimes and high ozonedepletion potentials, and will be phased out of production under the terms of the Montreal Protocol and other regulations.
Although it is relatively easy to identify chemicals having one, two, or three selected properties, it is very difficult to identify chemicals that possess simul-taneously all of the following properties: effective performance, nonflammability, low toxicity, cleanliness, electrical nonconductivity, miscibility with common lubricants, short atmospheric and environmental lifetimes, zero ODP, and very low GWP. Furthermore, the unusual and desirable properties of selected members of the obscure class of fluoroiodocarbons are by no means obvious. Fluoroiodocarbons have only rarely been studied, and very few of their properties are reported in the literature. Conventional chemical wisdom indicates that iodine-containing organic compounds are too toxic and unstable to use for these purposes, and iodocarbons have been rejected on those grounds by the majority of those skilled in the art. Partly as a result of this prejudice, the properties of the class of fluoroiodocarbons have been investi-gated only slightly, and fluoroiodocarbons have remained a little-known class of chemicals.
An important part of this invention is recognizing that the unique properties of fluorine (the most electronegative element) strengthen and stabilize a carbon-to-iodine bond sufficiently to render selected fluoroiodocarbons relatively nontoxic and stable enough for use in solvent cleaning, refrigeration, foam blowing, and aerosol propulsion. Painstaking collection and estimation of properties and screening for expected effectiveness, low toxicity, and low environmental impact have been carried out to identify them as being suitable for these new uses. Disclosed herein therefore are both new uses and new combinations of chemicals, leading to new and unexpected results.
Both the neat and blended fluoroiodocarbons described herein provide new, environmentally safe, nonflammable refrigerants, solvents, foam blowing agents, aerosol propellants, and firefighting agents. These compounds have the characteristics of excellent performance, cleanliness, electrical nonconductivity, low toxicity, nonflammability (self-extinguishment), short atmospheric lifetime, zero ODP, low GWP, and negligible terrestrial environmental impact.
Although some fluoroiodocarbons are described briefly in the known chemical literature, their potential for the uses described herein has never been previously recognized. No fluoroiodocarbons have been used before for solvent cleaning, refrigeration, foam blowing, or aerosol propulsion, either in neat form or in blends. One neat fluoroiodocarbon (CF.sub.3 I) has been briefly described as a firefighting agent in the open literature (Dictionary of Organic Compounds, Chapman and Hall, New York, 1982, p. 5477). A small number of additional neat fluoroiodocarbons has been proposed by one of the current inventors for use in firefighting (Nimitz et al., "Clean Tropodegradable Fire Extinguishing Agents with Low Ozone Depletion and Global Warming Potentials," co-pending U.S. patent application Ser. No. 07/800,532, filed Nov. 27, 1991). However, neither any blends containing fluoroiodocarbons nor the new neat fluoroiodocarbon agents described herein have ever before been proposed for use in firefighting or any of the other uses described herein. These blends and new neat agents offer substantial advantages in terms of lower cost, lower toxicity, improved physical properties, and greater effectiveness.